1. Field of the Invention
The present invention relates to a method and apparatus for controlling an air conditioner having a refrigerating circuit, especially, control apparatus for estimating an outside temperature in order to control the air conditioner.
2. Description of Related Art
An air conditioning unit typically has a refrigeration circuit which is composed of a compressor, a four way valve, an indoor heat exchanger, an expansion device and an outdoor heat exchanger. Some air conditioners require detection of the outside air temperature. For example, the following parameters can all be controlled in accordance with the outside air temperature: the speed control of an outdoor fan which circulates air past the outdoor heat exchanger, a current release control to control the speed of the compressor, a room temperature setting change control which corrects a room temperature setting in accordance with outside temperature in order to improve the comfort in the room and so on. These air conditioners therefore require an outside temperature sensor, for example a thermistor, bimetal or thermocouple sensor, which detects the outside air temperature.
One type of air conditioner includes the refrigeration circuit in a single case. In such an air conditioner, the outside temperature sensor is attached outside of the air conditioner case. The location of the outside temperature sensor is selected so that the correct outside air temperature is detected, avoiding the influence of the air flow of the outside fan, sunlight and radiation from the outdoor heat exchanger. Furthermore, the outside temperature sensor should be kept dry from rain or snow because the sensor is an electrical device.
Another type of air conditioner has an indoor unit including an indoor heat exchanger, and a separate outdoor unit including a compressor, a four way valve, an expansion device and an outdoor heat exchanger. Refrigeration pipes connect the indoor unit and the outdoor unit to form a closed refrigeration circuit. In air conditioners with separate indoor and outdoor units, an outside temperature sensor is placed in the outdoor unit. In this case, whether or not the outside temperature sensor is subject to the influence of sunlight depends on the site of the outdoor unit. Therefore, the site to install the outdoor unit should be selected so that the outside temperature sensor accurately detects the outside air temperature. If the site of the outdoor unit is subject to strong sunlight, the outside temperature sensor will also be subject to the sunlight. The detected outside air temperature will be higher than the correct value. Thus care must be taken to determine the proper placement of the outdoor unit. However, many other factors influence placement of the outside unit.
To avoid the need for an outside temperature sensor, it is also known to estimate the outside air temperature on the basis of the temperature of the outdoor heat exchanger. The principal behind estimating the outside air temperature is that the outdoor heat exchanger temperature depends on the outside temperature. The estimate is carried out a predetermined period after the air conditioner starts. At that time, the outdoor heat exchanger temperature is detected, and the outside air temperature is estimated by correcting the detected outdoor heat exchanger temperature with a predetermined value. However, the outdoor heat exchanger temperature depends not only on the outside temperature, but also on air volume passing through the outdoor heat exchanger. Therefore, this approach does not estimate the correct outside temperature accurately.